Hey all,

Working on a 2011 4L V6 with 110k miles on it. In the last week or so I've been getting misfires on cylinder 2 and 3 when doing some heavy acceleration or going up hills.

Spark plugs were replaced 10k miles ago, I've replaced spark plug wires, ignition coil, fuel filter, and fuel pump and still no change in behavior.

Codes are P0300 P0302 and P0303. STFT on bank 1 and 2 hover around 0 (+/- 2%)at idle but go pretty much opposite directions going up hills or putting the engine under load. So one side will be running lean and the other side rich and ranging in 15% or more in one direction.

O2 sensors seem to be responding as expected so I don't think there's an issue there but have not been replaced.

Would appreciate any tips on what to look at next! Thanks

 

Welcome to the forum

Does the CEL(check engine light) Flash during the misfires?

You can try some injector cleaner, like Seafoam in the gas tank

2 and 3 don't share a coil in the coil pack
But do share a head gasket
I assume there has been no overheating

Rich fuel trims are expected when accelreating
Lean fuel trim on misfiring side of engine would also be expected because of the misfires
O2 sensors only see Oxygen
High oxygen in exhaust = lean
When a cylinder misfire no oxygen is burned up, so its dumped into the exhaust and O2 sees high oxygen
So lean is not a cause but an effect in your description

While its a pain, doing a compression test on all 6 cylinders would rule out mechanical issue, or find out it is an issue
Cold engine, remove all 6 spark plug first then test each cylinder and write down results
Compression test is not about high numbers but about the relationship of the numbers
4.0l SOHC should show 170+psi in each cylinder but this depends on the gauge and battery condition(cranking speed
But if you test all 6 then exact numbers don't matter as much because if 4 test as 150psi and the 2 misfiring cylinders test as 125psi then you found the problem, 2 cylinders are "not like the others"

 

Hey thanks for the warm welcome and all the information.

Yes, check engine light flashes during the misfires.

Ran through about half a tank with Techron in it and it hasn't changed anything.

You are correct the engine hasn't overheated. Had the thermostat housing replaced at the same time as the spark plugs due to a slow coolant leak I had about a month ago. Engine never overheated when the coolant leak was present either.

I appreciate the advance and kind of figured the compression test would be the next step. I'll try to get that taken care of this week and update with results.

 

I know its delayed but wanted to post an update on resolution.

Root cause was a clogged cat and got that replaced and now I'm back on the road.